A rotary shaft of a drive machine such as a turbine, or of a rotary electric machine such as a turbine generator is supported by hydro dynamic bearing devices (journal bearing devices). In recent years, in order to comply with demands for electric power in, for example, developing countries, the capacity of powertrains (a couple of turbine and generator) alone tends to be increased. According to this, the width or diameter of the bearing device supporting the rotary shaft also tends to be increased.
In the hydro dynamic bearing device that is used in the turbine or turbine generator, a bearing surface of a lower half of a main bearing is formed with a groove at the center of a bearing width and in a circumferential direction (for example, JP-A No. Hei 8-93769). In a case where the circumferential groove is not provided, along with an increase in the bearing width, a pressure receiving area of the shaft is increased to increase force that lifts the shaft up, and stability of the bearing tends to be lost. However, by the provision of the circumferential groove at the center of the bearing width, formation of a fluid film of lubricant oil is stimulated and the stability of the bearing can be maintained.
Moreover, JP-A No. Sho 62-67325 (Patent Literature 2) describes that, in a journal bearing used in a steam turbine or the like, in order to prevent a bearing inner circumferential surface from being eroded by vapour bubbles produced in lubricant oil, an inner circumferential surface of an upper half part of a bearing body is, for example, heat-treated to thereby enhance a surface hardness and homogenize a structure, or a hardened layer is formed on the inner circumferential surface of the upper half part of the bearing body by plating or the like.